Designing Polymeric Materials with Enhanced Thermal Transport and Tailored Thermo-Responsive Properties

Abstract

Polymers afford modular molecular designing thereby allowing development of polymeric materials with precisely tailored intrinsic properties as well as response to neighboring environment. This dissertation discusses molecular design strategies to develop amorphous polymers with enhanced thermal transport properties, and a bi-functional polymer-based nanocomposite with thermally tunable behavior.

In the first part, strategies to modulate polymer chain morphology, inter-chain interactions, and chain packing are explored to develop amorphous polymers with high thermal conductivities. The first system consists of a polymer blend of two mutually hydrogen-bonding polymers: one, a H-bond donor polymer with long flexible chains mixed with the second H-bond acceptor polymer with short and rigid chains. A high concentration of strong and homogeneously distributed H-bonds results in a locally extended morphology of the long flexible polymer and creates a percolating network of efficient thermal connections. In this system, thermal conductivity reaching up to 1.72 W/mK was achieved for nanoscale films, which is nearly an order of magnitude higher than that of typical amorphous polymers. In the second system of a weak polyelectrolyte, controlled ionization results in electrostatically-induced extended chain morphology, more compact chain packing, and chain stiffening which together promote enhanced thermal transport. In a system with predominantly ionized (~90%) chains, thermal conductivity reached up to 1.17 W/mK for nanoscale films, which was nearly 3.5 times higher than that in a completely unionized polyelectrolyte film (0.34 W/mK). Furthermore, thermal conductivities up to 0.62 W/mK was achieved in micrometer-thick films. Overall, the two strategies discussed in this dissertation present a significant breakthrough in molecular engineering of polymers to realize high thermal conductivities in amorphous systems.

In the second part, a unique polymer-graphene oxide (GO) nanocomposite film-based planar microfluidic device is presented. The fabricated devices were used for sorting circulating tumor cells (CTCs) by their on-demand capture within the device and their subsequent release. The polymer provides a thermally tunable capture or release functionality and acts as the matrix to hold the functionalized GO sheets, which in turn are the scaffolds for the cell-capturing anti-EpCAM antibodies. Combining the temperature-sensitive modality of the polymer with the sensitive GO-mediated cell capture functionality yields a device that enables the study of CTCs without many of the shortcomings of the past technologies. At room temperature, the device captured more than 80% of the CTCs at flow rates of 1-3 mL/h, and released more than 90% of the captured cells on cooling below the polymer’s lower critical solution temperature. Easy operationability of the devices affords their deployment for processing of clinical samples. Viable and structurally intact CTCs were successfully isolated from 10 out of the 13 metastatic breast and pancreatic cancer patient blood samples processed. The CTCs isolated from the blood samples of metastatic breast cancer patients were further analyzed by fluorescence in situ hybridization (FISH), a standard cytogenetic technique. Successful isolation of viable CTCs from clinical samples thus highlights the utility of the fabricated device in research and clinical settings.